The present invention relates to a linear guide bearing device and, more particularly, to a linear guide bearing device in which rolling members are disposed between a rail and a bearing.
Linear guide bearing devices have been generally used in apparatuses which perform rectilinear motion, such as machining centers, lathes, grinders, robots, precision X-Y tables, measuring apparatuses, manufacturing facilities for semiconductor devices and liquid crystal display devices, and convey facilities. A linear guide bearing device used for these apparatuses comprises a rail, a bearing rectilinearly moving on the rail, and rolling members disposed in rolling contact between the rail and bearing.
The rolling theory of a rolling bearing is applied to linear guide bearing devices. The Lundberg-Palmgen theory in rolling bearings is also applied to the rolling fatigue in linear guide bearing devices.
Techniques obtained in the process of development of rolling bearings are utilized for materials, heat treatment conditions, and the like used in linear guide bearing devices. For example, the oxygen content in steel is suppressed to reduce nonmetallic inclusions that become the start points of separation as in rolling bearings. As for heat treatment, induction hardening and case-hardening are performed to introduce residual compression stress in the surface in order to prolong the service life as in rolling bearings.
A variety of techniques obtained in the process of development of rolling bearings are exploited in linear guide bearing devices. Higher workability is required for materials used for linear guide gearing apparatuses than those used for rolling bearings. In particular, excellent cold working like rail drawing is required. A material having a high carbon content used in rolling bearings may not often satisfy workability required in linear guide bearing devices.
Induction-hardened steel or case-hardening steel has been used for both the rail and bearing in conventional linear guide bearing devices. For example, "Special Steel" (February Issue, 1990, pp. 33 to 36) discloses a linear guide unit in which induction-hardened steel containing 0.53 wt % of carbon and 1.5 wt % of manganese and having an oxygen content of 10 ppm is used for both the rail and bearing. "NSK Technical Journal" (No. 645, pp. 45 to 59) reports use of degassified case-hardening steel for both the rail and bearing.
Of these steel materials, induction-hardened steel is most popular at present as the material for linear guide bearing devices because it can be relatively and easily heat-treated. It is, however, difficult to obtain excellent service life characteristics when induction-hardened steel is used for both the rail and bearing.
Along with recent developments of high-performance, high-speed, and high-precision mechanical apparatuses, demand has arisen for improving the performance of linear guide bearing devices. Durability is one of the performances to be improved most. For this reason, when durability is required, case-hardening steel is mainly used.
Case-hardening steel is better durability than induction-hardened steel. The use of case-hardening steel makes the heat treatment process more complex than the use of induction-hardened steel and requires bulky heat treatment facilities. The manufacturing cost becomes higher than that in the manufacture of a linear guide bearing device using induction-hardened steel.